How to transfer weights between vertex groups on separate meshes
am dum dum and found the answer like 10 min later.

Answer was to use a Data Transfer modifier on the mesh, have both Backup Mesh and OG Mesh in the exact same position, then enable Vertex trasnfer thingy, select the mesh you wanna transfer weights to in my case "UwU -> Nyaa"
(apologies for custom theme, hopefully its understandable)


this means whatever weights are on the "UwU" vertex group will be transfered over the "Nyaa" group. now the reason they need to be exactly positioned is because its more of a weight projection transfer rather than a seamless transfer. 

Another useful and more practical method (suggested by moonboots in the comments, thanks!) is to use the "Transfer Mesh Data" tool, easiest way is to Search "Transfer Mesh Data" and once you click on it you will see similar settings than the modifier.

For transfering vertex groups make sure the active groups on both meshes are the ones you wanna transfer, way it works is transfering Active object's weight over to selected.